Process for the reduction of arylnitroalkenes



Patented Mar. 4, 1941' UNITED STATES PATENT OFFICE PROCESS FOR- THE REDUCTION OF ARYLNITROALKENES ration of Indiana No Drawing. Application November 15, 1935i,

Serial No. 304,550

8 Claims. (Cl. 260566) Our invention relates to a process for the reduction of arylnitroalkenes, and more specifically, to a method for the production of arylall zanones, arylalkanone oximes, and arylalkylamines.

The arylnitroalkenesmay be produced by the condensation of aromatic aldehydes and nitroparaiilns (Knoevenagel and Walter, Ber. vol. 3'7, p. 4502 (1904); Worrall, Jour. Am. Chem. Soc. vol. 56, p. 1556 (1934) Alles, Jour. Am. Chem. Soc. vol. 54, p. 271 (1932)). Compounds of this type are desirably reduced to form amino compounds, and more or less successful reductions have been obtained in the case of compounds such as omega-nitrostyrene, obtained by the condensation of nitromethane with an aromatic aldehyde. However, in the case of nitroalkenes of the type it has been found to extremely diflicult to effect satisfactory reduction. For example, Benzedrine (I-phenyl-Z-aminopropane) may theoretically be obtained by the reduction of 1- phenyl-2-nitropropene, but in practice it has Q may be successfully reduced to arylalkanones or arylalkanone oximes by a single stage reduction by meansof iron, and can be reduced to amino compounds of the Benzedrine type in a two-Stage reduction in which the initially obwill be evident from the following description. The initial reduction of our process is effected in aqueous solution in the presence of suflicient finely divided iron to effect thereduction of all of the nitroalkene. An acid need not be employed in conjunction with the iron, but if em- 5 ployed, the concentration of the acid will afl'ect the nature of the reduction process. With no acid or only low concentrations of acid the reaction product is predominantly the oxime, whereas in the presence ,of relatively high con- 10 centrations of acid the reaction product is predominantly the ketone. The mechanism of the reactions is not definitely known, but the following type reactions are probably involved:

'20 ZAR-CHr-C-R-t-2NH2OH-I-Fe304 As may be seen from the above reactions, an amount of iron equal to at least 1.5 mol per mol 30 of nitroalkene is required, and the amount required by one of the-equations is. 3 mols per mol of nitroalkene. At least the lower limit of 1.5 mol of iron should be employed to effect sat- 3 isfactory reduction, and we prefer, in general, 5 to use more than 3 mols of iron per mol of nitroalkene. .An excess. of iron is not harmful and it serves to insure ascomplete reduction as possible.

It. may also be seen from the above equations that at least 1 mol of water is required per mol of nitroalkene in order to secure reduction to the 'oxime. We prefer, however, to-utilize a considerable excess of water in order to obtain a. 45 mixture which can be satisfactorily handled, and agitated during the reaction. Other solvents can be employed in conjunction with water if desired. but these should preferably be miscible with water in order to maintain'a single the necessary catalytic material.

liquid phase and thus facilitate the reduction. The use of an organic solvent in conjunction with water may be an advantage in controlling the type of reduction product secured. Thus, it it is desired to obtain the oxime rather than the ketone, the use or an aliphatic alcohol in conjunction with water will tend to increase the ratio of oxime to ketone in the products.

Although the reduction to the oxime may be effected in the absence of any acid, we prefer to employ an acid in conjunction with the iron for reduction either to the oxime or .to the ketone.

Any acid may be utilized for this purpose, and

the term acid in this connection is to be construed as a material yielding hydrogen ions. In general, however, we prefer to employ a mineral acid such as hydrochloric acid or a relatively strong organic acid such as acetic acid. The concentration of acid employed will depend upon the nature of the product desired. If it is desired to produce predominantly the oxime, an acid concentration not substantially higher than 0.06 mol of hydrochloric acid per mol of nitroolefln should be employed, or the equivalent amount of another acid, as for example, 0.03 mol of sulfuric acid. Increasing concentration of acid will produce an increase in the ratio of ketone to oxime in the reduction product. Approximately 2 mols of hydrochloric acid per mol of nitro-olefin' will produce almost entirely the ketone with only a trace of the oxime or none at all. Intermediate concentrations of acid can of course be employed if itis desired to produce intermediate ratios of the two products.

When employing no acid in conjunction with the iron it is desirable to employ a small amount I of an iron salt as a catalyst, for example, ferric chloride. When acid is used in conjunction with the iron, on the other hand, no such catalyst is required since the initial reaction of acid with the iron in the process will produce some of The use of a catalyst in conjunction with acid will, however, eliminate the short induction period required for the formation of a salt by the action of acid on the iron, and for this reason it may be advantageous to employ a catalyst in addition to acid, especially for large scale operations. The amount of catalyst to be employed is not critical, amounts ranging from 0.01 mol to 0.10 mol per mol of nitroalkene being generally satisfactory. The reduction of nitroalkenes to ketones and oximes may be further illustrated by the following specific example:

Example I phenyl-2-nitropropene, for the various reductions are shown in the table below. In each case the mixture was agitated for a period of approximately hours in a vessel equipped with a reflux condenser. At the conclusion of this period, the mixture was made alkaline with sodium hydroxide solution and steam distilled. The products were recovered from the steam distillate, dried, and carefully fractionated in a rectifying column to determine the yield of phenylpropanone and of the oxime of phenylpropanone. The conversions to these products,

assasss based on original I-phenyl-Z-nltropropene, are shown in the table below:

Table Percent conversion based on phenylnitropropene Mule Mols Moll Mols 4 H 0 so vent C Fe Oxime oi Pkwy 23:22:- none H0116 28 0 0 2 0 0. 0 0. 0 28 0 0. 00' 2 0 20. 1 0.0 28 0 0 2 1 0. 00 40. 0 5. 2 28 0 0.06 2 0.00 45.0 3.7 23 0 0 2 0. 23 27. 4 24. 0 28 0 0 2 1 0. 40 23. 1 30. 5 2s 0 0. 0c 2 1 1.39 20. 2 41.1 28 .0 0.00 2 1.74 13.4 50.0 28 0. 0. 06 7. 15 1. 74 0. 0 75.0 28 0 0.06 7. 15 1 1.07 0.0 77.0 28 0 0 2 I 0. 10 32. 5 11. 3 28 0 0 2 0. 52 37. 5 10. 5 0 12.4 0.00 2 0.00 0.0 0.0 H 12.! 0.00 2 0.00 02.0 10.5 14 4.4 0.00 2 0.00 64.2 9.0 14 8.0 0.00 2 0.06 63.0 9.7

1 Hydrochloric acid. I Sulfuric acid. Acetic acid. Methyl alcohol.

I Ethyl alcohol. i

In the second stage of our reduction process I the oxime obtained in the first stage is further reduced to the amine. Any suitable means for reducing the oxime without undue hydrolysis may be employedior this purpose. Among these methods may be mentioned reduction with sodium amalgam and acetic acid, reduction with inc-- tallic sodium in alcoholic solution, and hydrogenation with a platinum, palladium or nickel catalyst. We prefer to employ hydrogenation with a nickel catalyst, and this process trated in the example below:

Example If Approximately 9 parts by weight of the oxime isilluse or phe'nylpropanona was dissolved in approximately 60 parts by weight of 95% ethanol, containing 5 parts by weight oi. a nickel catalyst;

prepared by dissolving aluminum from a nickelaluminum alloy by means of caustic alkali. The resulting mixture was sealed in a bomb under a hydrogen pressure of 1880 lbs. per sq. in. and re-'- duction was eflected for a period of 3% hrs. at a temperature of 25 0., at the conclusion of which period the pressure was found to have dropped 7 to approximately 1680 lbs. per sq. in. The pressure was then released and the catalyst removed by filtration. The filtrate was acidified with concentrated hydrochloric acid and the product was recovered by crystallization as the hydrochloride oi 1-pheny1-2-amino-propane (melting point M l-146 C.) A conversion of 78%. based on the original oxime was obtained. g

It is to be understood, of course, that the above examples are merely illustrative and do not limit the scope of our invention. Although our inven tion is particularly adapted to the production oi 1-pheny1-2-aminopropane of the arylnitroalkenes of the type ARCYH=C-R may be reduced in accordance with our process.

In this formula AR may represent any aryl group,

but preferably phenyl or substituted phenyl, and R. may represent any alkyl group. It will be ap- (Benzedrine) an parent to those skilled in the art that the procedures employed in the above examples could be modified in numerous respects, and the use of any such modifications or any equivalents which would naturally occur to those skilled in the art is to be considered within the scope of our invention.

Our invention now having been described, what we claim is:

1. In a process for the reduction of an arylnitroalkene of the type ,iR-cH=oB in which AR represents an aryl group and R represents an alkyl group, the step which comprises subjecting said nitroalkene, in the presence of water, to the reducing action of iron.

2. In a process for the reduction of an arylnitroalkene of the type N0: in which AR represents an aryl group and R represents an alkyl group, the step which comprises subjecting said nitroalkene, in the presence of water and an salt, to the reducing action of iron.

I" .i ;.-;,-p,...-i-; this reduction of an aryl nitroalkene of the type in which AR represents an aryl group and R represents an alkyl group, the step which comprises subjecting said nitroalkene, in the presence of water and a water-miscible organic solvent, to the reducing action of iron.

4. In a process for the reduction of an arylnitroalkene of the type in which AR represents an aryl group and R. repand an acid.

in which AR represents an aryl group and R rep-' resents an alkyl group, the step which comprises subjecting said nitroalkene, in the presence of water, to the reducing action of iron and a mineral acid.

6. In a process for the reduction of an arylnitroalkene of the type in which AP, represents an aryl group and R represents an alkyl group, to form primarily the oxime of the corresponding ketone, the step which comprises subjecting the said nitroalkene to the reducing action of iron in an aqueous medium having an acid content not substantially greater than 0.06 equivalent of acid per mole of nitroalkene.

7. In a process for the reduction of l-phenyl- Zmitropropene, thestep which comprises subiecting said 1-phenyl-2-nitropropene, in the presence of water, to the reducing action of iron 8. In a process for the reduction of l-phenyl- 2-nitropropene to' form primarily the oxime of phenylpropanone, the step which comprises subjecting said 1-phenyl-2-nitropropene to the reducing action of iron in an aqueous organic solvent medium having an acid content not substantially greater than 0.06 equivalent of acid per mole of 1-phenyl-2-nitropropene.

ALFRED G. SUSIE. HENRY B. HASS. 

